A. Technical Field
Fabrication of small circuits and circuit elements, e.g., large-scale integrated circuits (LSI) is realized through the one or more pattern delineation steps. In accordance with prevalent practice at this time, use is made of discrete masks which when finally processed, consist of apertured chromium patterns supported on glass substrates. Typically a set of six or more such masks are required for semiconductor circuit fabrication. They are utilized sequentially for replicating patterns in sensitive supported (resist) material on the semiconductor, following which the replicated pattern is utilized to define areas to be etched, plated, implanted, or otherwise processed. There is a growing technology which involves electron beam delineation to produce such masks with design rules of a few micrometers or less. Replication is generally accomplished with near u.v. light.
The expectation that economic and other considerations may lead to smaller design rules has focused attention on inherent limitations in presently used mask technology. Standing waves, interference and other limitations relating to wavelength have led to studies directed to the use of effectively shorter wavelength replicating radiation such as X-ray, electron flood, and short wavelength u.v. Anticipated yield loss due to registration difficulty with diminishing design rules is leading to evolution of a "maskless" technology known as "direct processing." In this technology, the primary pattern delineation is in resist layers made an intimate part of the device at each stage in fabrication. All such fine-line programs are dependent upon introduction of suitable resists.